1. Field of the invention
The invention is about a mobile communication system that uses the followings: a frequency division multiple access method (FDMA), a time division multiple access method (TDMA), and a code division multiple access method (CDMA) or time divided code division multiple access method (time divided CDMA). The invention is related to a mobile communication system which provides the implementations of a radio frequency spectrum sharing (hereinafter frequency sharing) and a time slot sharing within a frame (hereinafter time slot sharing).
2. Description of the related art
The mobile communication system, for example, includes a plurality of mobile stations and at least a base station. Examples of the mobile station includes an automobile communication equipment and a portable communication terminal. The base station communicates with the mobile station through a radio channel. An advancement in the future of mobile communication system is highly expected particularly for the frequency sharing and the time slot sharing of the FDMA, TDMA and CDMA methods, from the viewpoint of channel efficiency.
The frequency sharing by a different spreading codes has already been implemented in the CDMA method.
The following methods in mobile communication system are filed by us as patent applications: a time slot sharing by TDMA signals and time divided CDMA signals within the same time slot; and a frequency sharing and time slot sharing by TDMA signals and time divided CDMA signals within the same time slot. (U.S. Ser. No. 08/524974 Filed:Sep. 8,1995; PCT/JP96/03507, Filed:Nov. 29, 1996; PCT/JP97/01113 Filed:Mar. 31, 1997).
With regard to a system of sharing a plurality of CDMA signals, for example, is disclosed in U.S. Pat. No. 5,363,403 "Speed Spectrum CDMA Subtractive Interference Canceler and Method" (IDC, by D. L. Schilling et al., Filed: Apr. 22 1993). However, the patent specification does not disclose a system to handle time divided CDMA method.
With regard to an adaptive filter of the time divided CDMA method, for example, is disclosed in U.S. Pat. No. 5,511,068 "Mobile Communication System capable of Transmitting and Receiving a Radio Signal obtained by TDMA and CDMA without Interference" (NEC, by T. Sato, Filed: Dec. 6, 1994). However, the patent specification does not disclose the frequency sharing of CDMA signal and TDMA signal within a same time slot.
The problem with the conventional mobile communication system is that it does not mention an effective method for a channel sharing the various access methods. That is, it does not mention about a method of the frequency sharing and the time slot sharing by a plurality of TDMA signals, nor about a method of the time slot sharing by the time divided CDMA signals. In addition, for communication between the mobile station and base station, an effective method to assign the TDMA signals and time divided CDMA signals in each communication from the viewpoint of the communication quality of the whole system is not indicated.